The aims of the study were to: (1) investigate factors affecting calf birth weight (CBW) and gestation length (GL); and (2) determine risk factors associated with dystocia in 1019 Holstein heifers and cows in a tie stall dairy herd. Calf sex (CS), sire, and GL were related to CBW in primiparous and multiparous cows, with no significant effect of season, age of primiparous cows (AGE) or days in milk (DIM) of multiparous cows at conception. Gestation length was affected by CS in primiparous, with a shorter GL for female versus male calves (275.7 ± 0.5 vs. 278.3 ± 0.4; P < 0.001). Also, GL was shorter in multiparous cows that calved during the cold season compared to those that calved in mild or warm seasons. Primiparous cows had a higher prevalence of dystocia compared to multiparous cows (32.1 vs. 8.5%; P < 0.001), but it was highly variable depending on sire (24.4%-60.0% for primiparous and 0%-21.1% for multiparous). In conclusion, CS, sire, and GL were related to CBW, whereas GL was affected by CS in primiparous and season in multiparous. The CBW was the major factor affecting dystocia in primiparous cows, whereas sire and twin pregnancies were factors related to dystocia in both primiparous and multiparous cows.
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Vol. 96 • No. 2